#!/bin/bash -e

[[ -w / ]] || exec sudo env HOME="$HOME" "$0" "$@"

if [[ -z ${UNSHARE} ]] ; then
	mount_args=
	if type -P unshare >&/dev/null ; then
		UNSHARE=true exec unshare -m -- "$0" "$@"
	fi
else
	mount_args='-n'
fi
unset UNSHARE

mounts="proc sys dev dev/pts usr/portage usr/portage/distfiles"

chroot=${0%/*}
case ${chroot} in
	.) chroot=${PWD} ;;
	./*) chroot=${PWD}/${chroot#./} ;;
esac
cd "${chroot}"

do_umount() {
	mounts=$(mount | grep ${chroot} | awk '{print $3}' | tac)
	for m in ${mounts} ; do
		echo "unmounting $m"
		umount $m
	done
	if [[ -z ${mounts} ]] ; then
		echo "nothing mounted in ${chroot}"
	fi
	exit 0
}

while [[ -n $1 ]] ; do
	case $1 in
		-u) do_umount ;;
		-*) echo "unknown option $1"; exit 1 ;;
		*)  break ;;
	esac
done

maybe_mount() {
	local src=/$1 dst=${chroot}/${2:-$1}
	[[ -d ${src} ]] || return 0
	mkdir -p "${dst}"
	grep -sq "${dst}" /proc/mounts || mount ${mount_args} --bind "${src}" "${dst}"
}
for m in ${mounts} ; do
	maybe_mount ${m}
done

get_type() {
	case $(file "$1") in
		*x86-64*)         echo x86_64;;
		*"Intel 80386"*)  echo i386;;
		*32-bit*PowerPC*) echo ppc;;
		*64-bit*PowerPC*) echo ppc64;;
	esac
}
bin_dst=$(get_type bin/bash)
setarch=
if [[ -n ${bin_dst} ]] && type -P setarch &>/dev/null ; then
	setarch="setarch ${bin_dst}"
fi

if [[ ! -L etc/mtab ]] ; then
	rm -f etc/mtab
	ln -sf /proc/mounts etc/mtab
fi
etc="
	hosts
	locale.gen
	localtime
	resolv.conf
"
home="
	.inputrc
	.gdbinit
	.gitconfig
	.nanorc
"
for f in \
	$(printf 'etc/%s ' ${etc}) \
; do
	if [ -e "/${f}" ] ; then
		cp /${f} ${f}
	fi
done
for f in ${home} ; do
	cp ~/${f} root/${f}
done

unset LS_COLORS # format changes over time
[[ $# -eq 0 ]] && set -- env HOME=/root /bin/bash -l
exec \
	${setarch} \
	chroot "${chroot}" \
	"$@"